﻿/*
 * DotNetCrypt - an open source library of cryptographic algorithms for .NET
 * Copyright (C) 2009 David Musgrove
 * 
 * This file is part of DotNetCrypt.
 *
 * DotNetCrypt is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * DotNetCrypt is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

using System;

namespace DotNetCrypt
{
    /// <summary>
    /// Computes the <see cref="MD2" /> hash for the input data using this
    /// managed library. 
    /// </summary>
// ReSharper disable InconsistentNaming
    public sealed class MD2Managed : MD2
// ReSharper restore InconsistentNaming
    {
        private byte[] _checkSum;
        private byte _checkSumLink;

        static private readonly byte[] _substitutionTable = {
                                                                41, 46, 67, 201, 162, 216, 124, 1, 61, 54, 84, 161, 236,240, 6,
                                                                19, 98, 167, 5, 243, 192, 199, 115, 140, 152, 147, 43,217, 188,
                                                                76, 130, 202, 30, 155, 87, 60, 253, 212, 224, 22, 103,66, 111, 24,
                                                                138, 23, 229, 18, 190, 78, 196, 214, 218, 158, 222, 73,160, 251,
                                                                245, 142, 187, 47, 238, 122, 169, 104, 121, 145, 21, 178, 7, 63,
                                                                148, 194, 16, 137, 11, 34, 95, 33, 128, 127, 93, 154, 90, 144, 50,
                                                                39, 53, 62, 204, 231, 191, 247, 151, 3, 255, 25, 48, 179, 72, 165,
                                                                181, 209, 215, 94, 146, 42, 172, 86, 170, 198, 79, 184,56, 210,
                                                                150, 164, 125, 182, 118, 252, 107, 226, 156, 116, 4, 241, 69, 157,
                                                                112, 89, 100, 113, 135, 32, 134, 91, 207, 101, 230, 45,168, 2, 27,
                                                                96, 37, 173, 174, 176, 185, 246, 28, 70, 97, 105, 52, 64, 126, 15,
                                                                85, 71, 163, 35, 221, 81, 175, 58, 195, 92, 249, 206,186, 197,
                                                                234, 38, 44, 83, 13, 110, 133, 40, 132, 9, 211, 223, 205, 244, 65,
                                                                129, 77, 82, 106, 220, 55, 200, 108, 193, 171, 250, 36,225, 123,
                                                                8, 12, 189, 177, 74, 120, 136, 149, 139, 227, 99, 232,109, 233,
                                                                203, 213, 254, 59, 0, 29, 57, 242, 239, 183, 14, 102, 88, 208, 228,
                                                                166, 119, 114, 248, 235, 117, 75, 10, 49, 68, 80, 180,143, 237,
                                                                31, 26, 219, 153, 141, 51, 159, 17, 131, 20};

        private byte[] _internalState;
        
        /// <summary>
        /// Initializes a new instance of the <see cref="MD2Managed" />
        /// class using the managed library.
        /// </summary>
        public MD2Managed()
        {
            InitialiseState();
        }

        private void InitialiseState()
        {
            _checkSum = new byte[16];
            _checkSumLink = 0;
            _internalState = new byte[48];
            Count = 0;
        }

        /// <summary>
        /// Initializes an implementation of the
        /// <see cref="T:System.Security.Cryptography.HashAlgorithm"/> class.
        /// </summary>
        public override void Initialize()
        {
            InitialiseState();
        }

        /// <summary>
        /// Transforms a single block of bytes using <see cref="MD2" />.
        /// </summary>
        /// <param name="array">
        /// An array containing the block of bytes.
        /// </param>
        /// <param name="ibStart">
        /// The offset of the start of the block within the array.
        /// </param>
        protected override void TransformBlock(byte[] array, int ibStart)
        {
            for (int i = 0; i < 16; i++)
            {
                _checkSum[i] ^= _substitutionTable[array[ibStart] ^ _checkSumLink];
                _checkSumLink = _checkSum[i];
                _internalState[16 + i] = array[ibStart++];
                _internalState[32 + i] = (byte)(_internalState[16 + i] ^ _internalState[i]);
            }
            byte t = 0;
            for (int i = 0; i < 18; i++)
            {
                for (int k = 0; k < 48; k++)
                {
                    _internalState[k] ^= _substitutionTable[t];
                    t = _internalState[k];
                }
                t = (byte)((t + i) & 0xff);
            }  
        }

        /// <summary>
        /// Finalizes the hash computation after the last data is processed
        /// by the cryptographic stream object.
        /// </summary>
        /// <returns>
        /// The computed hash code.
        /// </returns>
        protected override byte[] HashFinal()
        {
            var block = new byte[0x10];
            var bytesRemaining = (byte)(0x10 - (Count & 0xf));
            var partIn = new byte[0x10];
            FinalBlock.CopyTo(partIn, 0);
            for (int i = Count & 0xf; i < 0x10; i++)
            {
                partIn[i] = bytesRemaining;
            }
            TransformBlock(partIn, 0);
            _checkSum.CopyTo(partIn, 0);
            TransformBlock(partIn, 0);
            Array.Copy(_internalState, 0, block, 0, 0x10);
            HashValue = block;
            return block;
        }
    }
}
